You will need a hex editor and the original THUG2.exe to convert your parks.
This process assumes you have the BASLUS park file. If your file name looks different, go to the bottom before you begin Step 1.
Step 1. Open the park with your hex editor.
Step 2. Hit Control + F and search for the values 0C 89 52 7C. Make sure you select values and not text string.
Step 3. Delete every value that is before 0C 89 52 7C
Step 4. Go to File -> Save as
Step 5. Locate the directory C:\Program Files (x86)\Activision\Tony Hawk's Underground 2\Game\Data\customparks.
Save the file as custom1.prk in this directory, and overwrite the previously named file.
Step 6. Launch THUG2.exe
Step 7. Go to Park Editor and load a pre-made park. Load the first pre-made park.
Step 8. Save as your own.
If you used a 3rd party converter to transfer your park to your desktop or you used GameShark/CodeBreaker/ARMAX, you will need to convert your park into X-Port2 format before you being at Step 1. Download an application called PS2 Save Builder, load your park into the program, and save as X-Port2.
The hex editor I prefer is HxD Hex Editor.
You can download a THUG2.exe
here
